Torque, Force, and Catapults

I know there are a variety of ways to analyze a catapult or trebuchet through physics.
What is the easiest way for middle to early high school kids to carry out some worthwhile analysis?
I'm thinking if we look at it like a lever, then we can calculate the net torque given the counter-weight, projectile weight and length of both arms. Can we then take this net torque and calculate the force it would impart to the projectile?

When my son was in the fourth grade, members of his class build trebuchets and catapults as a class project - and competed one spring day. I assisted him in building his trebuchet - which was done with very little calculations.
We also visited one of the more powerful trebuchets, the Yankee Siege. Interestingly, it was also designed and built without any modelling. It has since retired from competition.

Aside from the length of both arms, there is the sling length and (very important) the sling release angle. Also the initial position of the sling and the ability of the overall mass of the trebuchet which effects its ability to roll back and forth as the counter-weight drops.

Here is a link that allows you to model many (but not all) of those parameters: